The present invention generally relates to an inflator for an air bag or cushion and more specifically to the type of inflator known as a hybrid inflator.
It is known that if the early inflation rate of an air bag is too high, the resulting deployment forces can contribute to the possible injury of an occupant who is out of the normal seated (either driver or passenger) position. If, however, the air bag inflation rate is maintained at a relatively low value, primarily to reduce such deployment forces, full deployment of the air bag may not be timely achieved.
It has for some time been appreciated that one goal of air bag inflator design is to provide an inflator which initially has a relatively low or soft inflation rate (for a relatively few milliseconds) primarily to protect the out-of-position passenger, such as a standing child, who would be subject to large deployment forces and thereafter to rapidly increase the inflation rate of the air bag to cause rapid and full inflation. U.S. Pat. 3,758,131 illustrates one type of staged inflation device. The drawback of this inflator is that it utilizes three pyrotechnic elements. One element is used to open a burst disk to initiate inflation of an air bag by permitting inflation gas to exit in a cold unheated manner (cold inflation). Two other pyrotechnic elements are energized either simultaneously or sequentially to thereafter heat the stored inflation gas to provide increased, staged inflation or gas discharge rates of varying levels. In addition to the complexity of this design the cost of the inflator is prohibitive and also requires a three electronic activation circuits. The commonly owned U.S. Pat. No. 5,022,674 illustrates another type of hybrid inflator which using two pyrotechnic elements. While this patent shows a means for achieving various levels of air bag inflation by energizing each pyrotechnic element this type of inflator does not provide for a cold inflation capability. It is an object of the present invention to provide an inflator which using two pyrotechnic heating elements and one which includes a cold inflation capability.
Accordingly the invention comprises: an inflator comprising: a pressure vessel for storing a quantity of stored inflation gas under pressure. The pressure vessel means comprising a first burst disk and a seal disk both for selectively sealing same. The inflator including a gas release mechanism for permitting the controlled, staged release of the inflation gas at determinable inflation rates. The gas release mechanism including: a first pyrotechnic device, positioned outside of the pressure vessel and spaced from the first burst disk, including a piston moved into a disk piercing position to rupture the first burst disk in response to the buildup of pressure caused burning of a first quantity of propellant material. The bursting of the first burst disk permits the inflation gas to initially flow out of the pressure vessel at a determinable cold inflation rate, the piston thereafter provides a conduit to communicate the products of combustion of the burning propellent to the pressure means so as to increase the temperature of the inflation gas therein and thereby increase the rate of egress of the gas. The inflator also includes a second pyrotechnic mechanism, positioned outside of the pressure vessel and spaced from the seal disk, for providing, when activated, additional products of combustion arising from burning of a second quantity of propellent material, the products of combustion opening the seal disk and thereafter entering the pressure vessel to heat the inflation gas therein and thereby elevate the rate of egress and the amount of resulting pressure of the inflation gas above the rate and pressure achievable by the first pyrotechnic device.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.